Conventional fiberglass communications antennas intended primarily for mobile use such as in the Citizen's Band radio service are either fixed-tuned by the manufacturer or supplied with one of a variety of mechanisms for tuning. These tuning mechanisms typically vary the length of the antenna or vary the value of an inductance incorporated into the structure of the antenna. Another means employs a tunable network in the signal line adjacent the base of the antenna.
A so-called fiberglass antenna consists of a wire helically wound around a flexible fiberglass rod to provide an electrically long, physically short, and durable antenna. Such a construction is especially suited to low cost mobile antennas which are subject to extreme conditions of use. However, the typical fiberglass rod antenna cannot easily be tuned by the user by adjusting the length of the antenna or varying its inductance value because of its pecuiar construction. The only practical way a fiberglass antenna heretofore could be tuned was to cut it to a shorter length corresponding to the desired frequency as discussed for example in a procedure described on page 326 of the 1978 edition of the ARRL Radio Amateur Handbook published by the American Radio Relay League, Inc., Newington, Conn. This method necessitates supplying the antenna tuned to the lowest frequency, i.e., the longest wavelength, giving the user the single option to cut it to a shorter wavelength. Unfortunately, this provided for adjustment in only one direction. Moreover, if the user made a mistake and cut the antenna too short, a poorly tuned antenna was the result. Furthermore, the use of a tunable network coupled to an antenna is a relatively expensive means of providing the tuning capability to optimize reception or transmission. A tunable network is at a particular disadvantage at longer wavelengths where the components tend to be physically large and unsuited to low-cost techniques for manufacturing VHF and UHF networks such as strip line circuitry and the like.